1. Field of the Invention
The present invention relates to an apparatus with an ultraviolet (UV) source for UV heating and photochemical treatment of substrates, including semiconductor substrates, and a method for processing said substrates using said apparatus. It finds particular application in etching, cleaning, or bulk stripping of films or contaminants from the surface of a semiconductor substrate at temperatures of about 400xc2x0 C. or less for use in the fabrication of integrated circuits.
2. Description of the Related Art
In the processing of semiconductor substrates, including cleaning etching or other treatments, it is well known to use ultraviolet (UV) activated gases. U.S. Pat. No. 5,580,421 to Hiatt et al, incorporated herein by reference, describes an apparatus for processing a substrate with a UV activatable conditioning gas. In copending application Ser. No. 08/621,538 filed Mar. 25, 1996, incorporated herein by reference, a method of removing undesired material from a substrate using fluorinated gases is disclosed. In copending application Ser No. 08/818,890 filed Mar. 17, 1997, incorporated herein by reference, a method using UV/halogen for metals removal is disclosed. Because chemical reaction rates are generally temperature dependent, the efficiency of a treatment can be dependent on the temperature at which the treatment is run. It can be desirable to preheat a substrate in a well controlled manner to a preferred process temperature above ambient temperature to provide enhanced process performance. Heating may also be used to thermally desorb volatile species adsorbed on the surface of a substrate.
There are a number of ways of heating a substrate in preparation for chemical processing or for thermally desorbing volatile species. The conventional way of heating, placing the substrate directly on a heating element, does not allow for access to both sides of the substrate. This can pose a problem in particular where one wishes to process both sides of a substrate. This also does not allow for multitemperature sequences with reasonable throughput.
Another way of heating a substrate is by applying a heated gas to the substrate. The use of a heated gas to heat a substrate is inefficient, however.
Yet another way of heating a substrate is via the application of infrared (IR) radiation to the substrate as in rapid thermal processing. However, if both heating and UV illumination are required this introduces considerable engineering difficulties, adding to the expense of any processing tool so equipped. These difficulties include control over stray chamber heating, control over the substrate temperature, and the logistics of incorporating an IR bulb, a UV bulb, and their respective control systems together in an apparatus.
The drawbacks of the above heating methods in the treatment of semiconductor substrates highlight the need for an inexpensive method to uniformly heat substrates to a desired process temperature and provide UV illumination in a single apparatus.
It is a goal of the present invention to provide a novel apparatus for heating and phototreatment of a silicon containing substrate that overcomes the problems associated with the above-mentioned methods of heating by exploiting a UV source present for phototreatment of a silicon containing substrate to also heat the substrate. The apparatus of the present invention comprises a reaction chamber for receiving and holding the substrate, a UV radiation source configured to direct radiation at the substrate, and a control system for controlling the UV radiation source. The UV source is capable of providing UV output of at least two different time averaged power levels, a heating level being effective to induce heating of the substrate and a photochemical level being effective to induce said phototreatment. Optionally, the present invention further comprises a chemical delivery system to deliver chemical into the reaction chamber. The present invention may also include at least one UV transparent window through which the UV radiation may be transmitted into the chamber.
In one embodiment of the present invention, in which a first UV lamphouse is mounted on the front side of the reaction chamber and a second UV lamphouse is mounted on the back side of the chamber, a substrate may be heated uniformly on both sides by directing UV radiation at both the front and back sides of the substrate simultaneously. In another embodiment, one side of the substrate is subject to UV at a heating level and the other side of the substrate is subject to UV radiation at a photochemistry level. In yet another embodiment, a single UV source is used for both heating and photochemistry.
It is a further feature of the present invention to provide a method for processing a substrate by heating the substrate to a temperature above ambient in one or more heating steps via UV output of a first time averaged power level, the heating level, and conditioning the substrate in one or more treatment steps by exposing the substrate to a photochemically (UV) reactive chemical in the presence of UV radiation at a second time averaged level, the treatment level, which is distinct from the the first heating level. A photochemically reactive chemical is broadly defined to include those chemicals which become photoactive due to an interaction, such as adsorption on the surface of the substrate. A photochemically reactive chemical is also defined to include species already adsorbed on the surface of the substrate which are caused to photodesorb due to the presence of the impinging UV radiation.
It is a further feature of the present invention to provide a method for processing a substrate by heating the substrate to a temperature above ambient in one or more heating steps via UV output in the absence of a photochemically reactive gas and conditioning the substrate in one or more treatment steps by exposing the substrate to a photochemically (UV) reactive chemical.
The present invention further pertains to a method for performing a UV photochemical treatment on a semiconductor substrate, comprising at least one heating step in which UV radiation is provided to at least a portion of the substrate at a total radiative power density, integrated from 0.1 to 1.0 microns of wavelength, of 0.3 watts/cm2 or higher, and at least one reaction step in which UV radiation at a power level distinct from the heating power level is provided, the UV radiation interacting with at least one photochemically reactive chemical causing a chemical reaction effecting a treatment of the substrate, wherein the power density in the heating step exceeds the power density in the reactive step.
The present invention allows for increased flexibility in treating substrates in that the UV phototreatment and UV heating can be directed independently to one or both sides of the substrate. For example, the front side of a substrate can be protected from direct UV illumination if only gas phase activation is desired. Moreover, because stray heating of the treatment chamber associated with IR heating is reduced to a great extent with a UV heating system, the need for a complex and expensive chamber cooling system is eliminated while a high throughput can be maintained.